1. Field of the Invention
The present invention relates to a sliding unit adapted for use in, for example, machine tools, assembly machine, testing instruments or the like, and more particularly a sliding unit having sealing means for keeping relatively sliding regions from the contamination of foreign materials such as dust and dirt.
2. Description of the Prior Art
The recently remarkable development in mechatronics technology requires increasingly the general-purpose sliding units. Although the sliding means or units have been now employed extensively in various fields such as machine tools, semiconductor manufacturing apparatus, transportation apparatus, industrial robots and the like, the need of the sliding units extends into many technical fields. With the expansion of uses, the sliding units become required more and more to deal with the precision, high-speed moving, easy assemblage, wide applicability and the like.
The sliding unit is in general comprised of a track rail mounted on a machine bed or the like, a sliding element such as a workpiece table movable along the track rail, and a driving mechanism for moving linearly the sliding element on the track rail. The driving mechanism is, for example, comprised of a screw shaft drivingly mating with a screw nut fixed to the sliding element, supporting brackets for bearing the screw shaft at its lengthwise opposing ends, and driving means such as a motor mounted to any one of the supporting brackets so as to rotate the screw shaft. On the sliding units of the type described above, the sliding element, or the slider, may be either positioned on the track rail or guided along the track rail by electrically controlling the driving means.
Shown in FIGS. 12 to 14 is the sliding unit disclosed in Japanese Patent Laid-Open No. 30234/1999.
The sliding unit 1 in FIGS. 12 to 14 is primarily comprised of an elongated track rail 2 having an U-shaped traverse cross-section, a sliding element 3 movably accommodated in an U-shaped recess 5 of the track rail 2, a screw shaft 4 mating with the sliding element 3, and a driving motor 9 for rotating the screw shaft 4. The screw shaft 4 is supported for rotation in first and second bearing members 11, 12 at the lengthwise opposing ends of the track rail 2. The motor 9 is mounted to the first bearing member 11 near the motor and the track rail 2 is fixed to a base by means of any suitable means such as screws. The sliding element 3 is constructed so as to move linearly on the track rail 2 through, for example, a linear motion guide mechanism. A bottom 6 and a pair of upright side walls 7 define in combination the U-shaped recess 5 in the track rail 2. The side walls 7 are provided on their widthwise opposing inner surfaces 33 with raceway grooves 8 that extend in parallel with each other lengthwise along the track rail while the sliding element 3 has raceway grooves, not shown, confronting the raceway grooves 8. Rolling elements may run through raceways, which are defined between the raceway grooves 8 on the wide walls 7 and the raceway grooves on the sliding element, thereby making the sliding element 3 move smoothly on the track rail 2.
The sliding element 3 has a pair of widthwise opposing upright flanges 13, which are to mount an object such as a workpiece table, not shown, on the sliding element. The flanges 13 are formed with threaded holes 14 for fixture means such as screws. A dustproof cover 15 is attached to the bearing members 11, 12 by means of fixing bolts so as to shield the track rail 2.
The dustproof cover 15 extends over the driving mechanism of the sliding unit 1, that is, the sliding element 3 and the screw shaft 4 accommodated in the track rail 2 to protect the driving parts from foreign bodies that might otherwise fall on or invade into the driving mechanism. The dustproof cover 15 is further formed with matching holes in alignment with the locations where the fixing bolts are driven. A pair of the upright flanges 13, on which the object to be moved is loaded, is formed so as to unobstructively face the dustproof cover 15. To this end, the upright flanges 13 each extend widthwise outwardly of the sliding element 3 and then turn upwardly to thereby provide a substantially L-shape in front view. The object such as a workpiece table is mounted on the flanges 13 with bolts that fit in matching holes 14. As will be seen from the foregoing, relatively moving the sliding element 3 to the track rail 2 causes the object mounted on the sliding element 3 to traverse with respect to the base.
Fixed to the sliding element 3 with screws 18 is a nut 17 formed with an internal helical groove that mates with an external helical groove provided around the periphery of the screw shaft 4. The combination of the screw shaft 4 with the nut 17 constitutes a torque-to-thrust conversion mechanism in which the rotation of the axially fixed screw shaft 4 results in driving linearly the rotationally fixed nut 17 along the track rail 2. To help ensure the reliable smooth linear movement of the sliding element 3, rolling elements are loaded so as to run in a circulating manner between the confronting helical grooves of the screw shaft and the nut whereby the torque-to-thrust conversion mechanism is designed as a ball nut and screw shaft assembly, which is comprised of the screw shaft 4, nut 17 and circulating rolling elements. The sliding element 3 is provided on its widthwise opposing side surface with raceway grooves to form raceways for running the rolling elements in cooperation with the raceway grooves 8 in the track rail 2. In addition, the casing of the sliding element 3 includes therein return-paths for the rolling elements.
Fixed on railheads 20 of the side walls in the track rail 2 with screws are bearing members 11, 12 that support the screw shaft 4 for rotation at its lengthwise ends. The raceway grooves 8 and the railheads 20 in the track rail 2 are finished in parallel with each other. Therefore, simply fixing the bearing members 11, 12 on the railheads 20 of the track rail 2 with horizontal position alignment may be sufficient to arrange the screw shaft 4 on the track rail 2 in the sliding element 3 in accurate alignment with the moving direction of the sliding element 3, with no necessity of vertical position adjustment.
Sensor rails 21 are disposed widthwise outwardly of the side walls 7 of the track rail 2 and bolted at 22. Sensors 23 are arranged on the sensor rails 21 at positions that are to be identified such as the beginning. Signals issued from the sensors 23 that have detected the flanges 13 are input to a controller unit, not shown, through a lead wire 24 and a sensor connector 25 and then control signals from the controller unit are applied to the motor 9 such as a stepping motor.
As shown in FIGS. 12 to 14, the sensor rails 21 are each provided therein with a furrow 26 extending along the lengthwise direction of the rail, in which may be kept the lead wire 24. Further, the sensor rails 21 form side covers 27 to shield the track rail 2 and the sliding element 3 on their widthwise-opposing sides. Formed at the bottom 6 of the track rail 2 are holes 29 matching with bolts to fix the track rail 2 onto the base. The holes 29 are bored in tow rows and spaced apart from each other with a predetermined distance. The torque of the motor 9 is transmitted to the screw shaft 4 through a coupling 30. The permissible span of the reciprocating movement to the sliding element 3 is defined with stoppers 31, 32 that are secured to the bearing members 11, 12, one to each bearing member.
In the meantime, as the flanges 13 on which the workpiece table is to be mounted move integrally with the sliding element 3, the sliding unit 1 of the type as described above is necessarily provided with gaps or clearances L for permitting the movement of the flanges 13 therethrough. Although the sensor rails 21 constitute the side covers 27 that partly conceal the relatively sliding region, no design is proposed for substantially completely shield the gaps or clearances L and, therefore, the prior art makes it impossible to keep completely the sliding unit 1 from foreign bodies that invade into the driving mechanism through the gaps or clearances L.
To cope with the antinomic problem in the prior sliding unit, wherein the flanges are allowed to move unobstructively while the interior of the sliding unit may be effectively purged of the invasion of foreign bodies such as dust and dirt, the inventor has considered employing a expansible sealing members that close normally the gaps open between the dustproof cover and the track rail and may be elastically collapsed so as to form slits for permitting the movement of the flanges, on which the object is to be mounted, with the passage of the flanges.